Introduction to Primary Production, Respiration and Nutrient Cycling –Cont. 1)REVIEW 1)Why we care? A)Coupling of atmosphere and ocean 2)Ocean carbonate system & importance to chemistry in the of sea water 3)Processes in controlling distribution of oxygen & dioxide in the ocean. 4) Ocean circulation and oxygen, carbon dioxide and nutrients Oscar Schofield

THYLAKOIDMEMBRANE STROMA CYTOSOL LHCLHC 1/2 O 2 + 2H + H2OH2O 4Mn Yz e-e- 2H + PQ QbQb QbQb Cytochrome b 6 -f-Fe nn 2H + PC/ cyt c 6 Photosystem I CHLOROPLAST P700 A0A0 FxFx Fa/ FbFa/ Fb FdFd ATP synthase complex CF 0 CF 1 3/2ADP + 3/2Pi 3/2ATP + 3/2Pi NADPH H + + NADP + 6H + 1/2CH 2 O + 3/2ADP + 3/2Pi H + + 1/2CO 2 THYLAKOID LUMEN E P680 Pheo e-e- e-e- Photosystem II D2 D1 E QaQa QbQb 2 x e - PH Minutes to Hours NUCLEUS P LHC gene Repressor proteins Days to Weeks fluorescence

light intensity oxygen evolution quantum yield of oxygen evolution Pmax  I k = Pmax/ 

OKAY: Ocean Photosynthesis occurs Why do you care?

t Processes/Platforms: Time and Space Scales Dickey, 2001a

OCEANOGRAPHY IS FRIGGIN’ HARD

Stewart et al., 1998 Monthly mean sea level at San Francisco ( ) Annual averages of sea level at Venice and Trieste ( ) (from N.Gruber)

Respiration Photosynthesis CO 2 O2O2 O2O2

Abundance of Gases in Air and Seawater and Gas Exchange In addition to dissolved salts, organic molecules and suspended solids, sea water contains dissolved gases. Most of these gases enter the sea from the atmosphere, but others are produced within the ocean by marine organisms or are derived from the Earth’s interior (e.g. helium). CO 2 O2O2 O2O2 CH 3 He Diffusion or gas exchange

There will be a net uptake (or loss) of a gas by sea water from the atmosphere until the sea water reaches saturation. At saturation, the gas exchange process is said to be in equilibrium, i.e. the rates of exchange in and out are equal. Bud time Bud

Saturation values are gas concentrations when a solution (here we are concerned with sea water but the term applies to any solution) has reached equilibrium with its overlying gas mixture (here the atmosphere). That is, saturation values are the most chemically favorable conditions. Since some gases are more soluble than others, the proportion of gases dissolved in saturated sea water is different from the proportion in the atmosphere Ar CO O2O N2N2 Proportion in saturated sea Proportion in Air Gas at 15 C and 35‰ The gas solubilities of CO 2 > Ar > O 2 >N 2

A saturation value depends on: -temperature (boiling water) -salinity (boiling water) Generally, cold water can hold more dissolved gases than warm water of the same salinity, and fresh water can hold more dissolved gases than salt water of the same temperature. ConditionsSaturation Conc. for O 2 (  mol/kg) Freshwater (25 o C)258 Seawater (25 o C)206 Freshwater (5 o C)398 Seawater (5 o C)308

Carbonate System Although CO 2 is a soluble gas in sea water, it also reacts chemically with water and is present in sea water as a one of two dissolved anions, bicarbonate and carbonate, and as carbonic acid. FORMS of CARBON DIOXIDE IN SEA WATER carbon dioxide CO 2 (dissolved) carbonic acid H 2 CO 3 bicarbonate HCO 3 - carbonate ion CO 3 2-

Reactions 2 and 3 (below) are acid-base reactions. Bicarbonate ion which is one of the major ions in sea water can act as both an acid and a base. 1). CO 2 + H 2 O H 2 CO 3 2). H 2 CO 3 + H 2 O H 3 O + + HCO 3 - acid base acid base 3). HCO H 2 O H 3 O + + CO 3 2- acid base acid base pH is a short hand scale for representing the acidity or alkalinity of a solution which depends on the concentration of hydrogen ions (H + ) (or hydronium ions, H 3 O + ) in the solution. pH = - log (H + )

The carbonate system is largely responsible for maintaining seawater pH close to a value of 8. i.e., slightly alkaline. This is largely because in the ocean, sea water is also in contact with sediments that contain carbonate minerals the most important of which is calcite (CaCO 3 ). If excess acid is added to the deep ocean (say for example via hydrothermal vent emissions) the acid is neutralized by reacting with carbonate ions in solution, and these are replaced by dissolution of carbonates in the sediments. If excess base is added more carbonate minerals precipitate and and are removed to the sediments.

Respiration Photosynthesis CO 2 O2O2 O2O2

phytoplankton need: light CO 2 nutrients water In the ocean, light and nutrient availability may limit the rate of photosynthesis. THE MAJOR FORESTS IN THE SEA ARE PHYTOPLANKTON

In the text, photosynthesis is represented very simply. It can be represented more completely, if we think of it as a process that generates the organic matter in phytoplankton cells. Phytoplankton organic matter is made up of a large number of organic compounds (e.g. proteins, lipids, carbohydrates), but on average it has atomic ratios of C to N to P of 106 to 16 to 1. Thus, the process of photosynthesis can be represented as: hv 106CO H 2 O + 16HNO 3 + H 3 PO 4 (CH 2 O) 106 (NH 3 ) 16 H 3 PO O 2 This reaction illustrates the need for the nutrients: nitrate and phosphate. It also shows that for every 106 CO 2 molecules taken up, approximately 138 O 2 molecules are liberated.

Irradiance Intensity Z (meters) IkIk Photosynthesis Biomass Nutrients

In the photic zone, photosynthesis leads to high oxygen concentrations and low total-CO 2. When photosynthesis rates are high, oxygen concentrations can rise above saturation. This is a state called supersaturation. Marine bacteria, fungi, protozoans and animals that can not get energy from photosynthesis, decompose organic matter. This process is called respiration. It can be represented as the reverse of photosynthesis. (CH 2 O) 106 (NH 3 ) 16 H 3 PO O 2 106CO H 2 O + 16HNO 3 + H 3 PO 4 Respiration puts CO 2 and nutrients back into the water. Respiration depletes O 2, making deep waters undersaturated with respect to the oxygen in the atmosphere. Respiration occurs throughout the entire water column and in sediments, but its effect on the distributions of oxygen and total-CO 2 are usually not seen until depths below the euphotic zone.

Depth Distributions of Oxygen and Total-CO 2 / Light/ Photosynthesis and Respiration In the upper ocean, these two profiles appear almost as mirror images. This is because both oxygen and carbon dioxide are involved in the production and destruction of organic matter, i.e. the soft tissues of marine plants and animals. CO 2 is also taken up by some plants and protozoa to make calcium carbonate (CaCO 3 ) hard parts. Since these shells dissolve at depth in the ocean, total- CO 2 profiles may not co-vary as closely with oxygen profiles at depth. The greatest changes in oxygen and total-CO 2 occur in the uppermost ~80 m of the ocean. This depth range corresponds to euphotic zone, the zone where there is sufficient light for phytoplankton (single celled plants that have chlorophyll) to grow through the process of photosynthesis.

The Biological Pump About 10% of the carbon fixed by photosynthesis in the surface layer each year, escapes this layer by sinking into the deep ocean. This flux is called New Production or Export Production. Physical mixing processes Nutrients Irradiance Phytoplankton Sinkage & Senescence Sinkage & Senescence Particle Dynamics Carbon Flux Zooplankton Higher Trophic Levels Nutrients Biologically derived nutrients New production Regenerated production Export production

The biological pump is an important mechanism for removing fossil fuel CO 2 from the atmosphere into the ocean because Sequestration of Atmospheric Carbon Nearly all of the sinking particulate organic matter is converted back to CO 2 through respiration in the deep ocean. Photosynthesis followed by a) the transport of carbon into the deep ocean and b) the respiration of the majority of this carbon, is called the "biological pump".

The biological pump is an important mechanism for removing fossil fuel CO 2 from the atmosphere into the ocean because 1. it lowers surface CO 2 concentrations, and 2. it transports particulate carbon into the deep-ocean, where even if it is oxidized back to CO 2, it is removed from contact with the atmosphere for on the order of 500 years. Models show the pump is doubly important at high latitudes because here the waters of the deep ocean are formed. First of all cold waters have higher saturation values for gases than warm. Then if primary production rates are high too, even more CO 2 will exchange from the atmosphere to the cold surface waters of the arctic and antarctic regions. The sinking of this water "captures" the CO 2 and removes it from contact with the atmosphere.

Ocean circulation eventually brings the respired CO 2 back to the surface, but the net effect is to keep the deeper ocean enriched in dissolved inorganic carbon. Pacific Ocean CO 2 rich water CO 2 off gas (bud)

Geographic Differences in Nutrient Profiles

(Takahashi et al 1995) Net CO 2 flux

SeaWiFS Team/GSFC/NASA Surface distribution of chlorophyll a using SeaWiFS data sets: Note physical forcing effects: Coastal, Equator, North Atlantic

Nutrient Limitation Many elements are necessary for life, but only those in short supply are limiting to photosynthesis. Oceanographers consider nitrate, phosphate, silica, iron and several other trace metals to be the most biolimiting elements. Silicon is important for the growth of diatoms. Iron is required for photosynthetic electron transport and the synthesis of chlorophyll. Nutrient profiles generally increase with depth. Concentrations may be below detection in surface waters, especially in the open ocean.

Nutrient sources to surface waters are: rivers and land runoff upwelling atmosphere The most productive regions of the oceans are the coastal regions because this is where upwelling is strongest and where river and land runoff meet the sea. Here nutrients result in high productivity rates, which in turn result large fisheries.

40N 74W75W 39N Temperature o C July 6, ’98 - AVHRR Field Station LEO 40N 74W 75W 39N Field Station Chlor-a (mg/m 3 ) July 11, ‘98 - SeaWiFS LEO Barnegat Cape May New Jersey Coastal Upwelling Historical Hypoxia/Anoxia

Geographic Differences in Nutrient Profiles